This invention relates to the technology of heat-sensitive recording using the thermal head. The invention particularly relates to a heat-sensitive recording apparatus capable of quiet recording.
Heat-sensitive recording is used as a means of recording with various types of printer, plotter, facsimile, recorder, etc. Heat-sensitive recording has various advantages such as no need for wet development and ease of handling, so its application to image recording for medical diagnoses that require large and high-quality image as in CT, MRI and X-ray imaging is currently being studied.
As is well known, heat-sensitive recording uses a thermal head having heating elements arranged in one direction (the main scanning direction); with the thermal head being slightly pressed onto the heat-sensitive material, the two members are moved relative to each other in the auxiliary scanning direction which is normal to the main scanning direction and in accordance with the image to be recorded, the heating element for each pixel is supplied with energy to generate heat so that the recording layer of the heat-sensitive material is hated to record image.
The heating elements (heat generating resistors) are usually arranged as tiny projection or elevation called xe2x80x9cglazexe2x80x9d that extend in the main scanning direction.
In heat-sensitive recording with the thermal head, a transport roller called xe2x80x9cplaten rollerxe2x80x9d is commonly used to hold the heat-sensitive recording material under given pressure between itself and the thermal head; as the platen roller rotates, the thermal head is urged with the heat-sensitive material being held in a predetermined recording position and, at the same time, the heat-sensitive material is moved relatively in the auxiliary scanning direction to perform thermal recording.
During such thermal recording, the surface of the heat-sensitive material is melted upon heating and gets xe2x80x9cstuckxe2x80x9d to the thermal head upon cooling. As already mentioned, during thermal recording, the thermal head and the heat-sensitive recording medium are transported relative to each other in the auxiliary scanning direction as they are pressed together. Therefore, during thermal recording, the heat-sensitive material repeatedly gets stuck to and separates from the thermal head and xe2x80x9crecordingxe2x80x9d sound is produced as these phenomena occur.
Needless to say, printers should produce smaller xe2x80x9crecordingxe2x80x9d sound. In case of medical heat-sensitive recording apparatus which is often used in hospitals, the recording sound should be as small as possible in order to cause no greater stress to patients and doctors while ensuring that treatments can be done undisturbed. In medical applications, it is required to output hard copies having as high image quality and definition as X-ray films. To meet this requirement, the medical heat-sensitive recording apparatus uses a heat-sensitive material in the form of a double weight (heavy-gage) film and the thermal head is also urged at higher pressure during thermal recording. Since this requires a higher torque to transport the heat-sensitive material, the medical heat-sensitive recording apparatus which should be quieter than non-medical types will nevertheless produce greater xe2x80x9crecordingxe2x80x9d sound.
The present invention has been accomplished under these circumstances and has as an object providing a heat-sensitive recording apparatus that produces small enough xe2x80x9crecordingxe2x80x9d sound to permit quiet heat-sensitive recording with a thermal head even if the heat-sensitive material is transported under high torque during recording as is often the case in medical applications.
In order to attain the object described above, the present invention provides a heat-sensitive recording apparatus comprising: a thermal head with heating elements arranged in one direction; a transport unit by which the thermal head and a heat-sensitive recording material being pressed by it are transported relative to each other in a direction normal to the one direction in which the heating elements are arranged; and a drive unit that disperses image data for one pixel into a-specified number of pieces and which drives the heating elements in the thermal head in accordance with the dispersed image data to perform heat-sensitive recording; wherein the heat-sensitive recording by means of the drive unit satisfies T/nxe2x89xa650 xcexcsec, where T is a period of recording the one pixel and n is the specified number of pieces into which the image data for one pixel is dispersed.
Preferably, the heat-sensitive recording in accordance with the dispersed image data is multi-gradation heat-sensitive recording by pulse width modulation.
Preferably, the image data for one pixel is dispersed in such a way that respective pieces of dispersed image data are allocated in a generally uniform manner.
Preferably, successive cycles of dispersed recording of the one pixel are interrupted by a period during which no heating element is driven.
Preferably, dispersed recording of the one pixel is such that cycles of heat-sensitive recording with the dispersed image data are started at specified intervals.